fix: Add timeouts to every tailnet ping (#4986)

A ping isn't guaranteed to deliver, so these need to have a
tight timeout for tests to not flake.

coderd/workspaceagents_test.go

@@ -179,6 +179,8 @@ func TestWorkspaceAgentListen(t *testing.T) {
 			_ = conn.Close()
 		}()
 		require.Eventually(t, func() bool {
+			ctx, cancelFunc := context.WithTimeout(ctx, testutil.IntervalFast)
+			defer cancelFunc()
 			_, err := conn.Ping(ctx)
 			return err == nil
 		}, testutil.WaitLong, testutil.IntervalFast)